Confusion and dissatisfaction in my sex / relationship life

Sorry if this is long but i'd appreciate any insight on a somewhat complex problem. I wan't to simplify things. So I currently have a wonderful girlfriend (we're almost 2 years into our relationship) and we've been through a lot of turmoil a few months ago involving unfaithfulness on both sides, but we've gotten past that and now if anything we're closer than ever. However, we met in College and after spending about 3 months together, she had to transfer and now it is very very hard and obstructive to my strenuous schedule to visit her. As much as I love to be with her, I have to rely on the drives of my friends (I have no car)and the train, which is dirty and unsafe (DART in Dallas) and of course that even makes the things we can do together somewhat limited. We take the bus and go to a movie, and dinner, and that might describe a typical night together. I'm a junior pre-med student at my school and I get so stressed out by how upset she gets when i cant visit her on a weekend, but I really don't like spending time in dallas, although I do go just to see her. I've been finding like I feel very coerced into seeing her and as much as like to do so, she's very attached to me and lately all i've wanted to do was be alone and away from her. It's worth noting though that Depression runs rampant in my family and i've starting on a short term medication for my lack of sleep and depression and also i've coupled that with therapy. I miss my family a lot, since i'm no where near them and lost my role model and idol (my father) to suicide a few years back. So in a lot of ways, i have a lot of things going on that really keep me from feeling okay, but i'm very confused about what to do with my girlfriend. In a way i feel stuck, I love and appreciate her, but i feel like seeing her is almost not worth the trouble (visiting her is stressful and we rarely get a moment away from her family). On another note, for about the third time now, a girl here with me at my school has made it clear she's very interested in me and i'm considerably attracted to her, even though it seems like she "gets around" she's made it clear she has genuine feelings for me, and I like her a lot. I've considered breaking up with my girlfriend several times, and i'm never really able to go through with it, especially without what seems like a real justification. All the same, I can't stop thinking about this new girl and through a combination of guilt, nervousness and lack of confidence we have not been sleeping together although i have had ample opportunity to do so. People around school see us together and think we are, and also she's come on to me several times but I just haven't felt right doing it. My therapist advises i don't make any major decisions for the next few weeks in terms of a breakup or anything of that sort but I just feel like a major part of my current relationship results from me feeling stuck, I feel like I lack the confidence to start something new and even now when I spend time alone with the new girl, i just feel like I never really know what to say or how to act, there's clearly a lot of sexual tension and I do want to see what's she's like but I just can't seem to make the right moves towards her. To be honest I do really think she's gorgeous and i'd really like to see what happens between us, but I am plagued by guilt and I do think this actually ties back to what has happened between my father and my family, but i just want to have the peace of mind to let things happen if they happen. The trouble is, the more i know she is interested in me the harder i feel it is to act natural, and as a result I really feel boring and weak around her, and this i find really upsetting, although In a way, having a girlfriend really adds to my reluctance to take things anywhere with her. The problem is, I get really really nervous around her, and just girls in general when I feel that sexual tension, I just don't feel confident in my ability to set the stage to take things further, and while i don't feel this stems from the fact that I already have a girlfriend (who i haven't made it to seeing in weeks), I want to have the peace of mind to do the things I want instead of half-assing my attempts with this new girl or any others (it happened on more than one occasion) but i've just never been comfortable at sex and relationships, I put a lot of pressure on myself to impress, and I always have. Anyways, I just want to get past this feeling of inadequacy and lack of confidence just enough so that I can go with the flow and figure out what I really want from either girl. I won't ever be satisfied with my current girlfriend unless I am confident I could make it with another girl or girls as well, and while it sounds a bit wrong, I don't like the idea of being so fearful about a breakup considering these things to do happen, and this is kinda why I feel stuck. Like I said, i'm going through a lot, but i've had a long talk with this new girl, we made out a little, but she could tell i wasn't really into it. Even still, i'm finding her on my mind a lot more than she should be at this point, and i don't know what to do, and i especially don't like to hurt people's feelings. A part of me wants to open up to my new friend and see how she really feels about it, but at the same time, It's almost my two year anniversary. I also feel that a lot of my frustration and sadness stems from this conundrum and my inability to make use of the chances i feel many other guys would jump to have the chance to. Any comments or insight about why i get so damn nervous around this new girl would be appreciated, i'm sure it's not just my girlfriend, but something else just gets me feeling so stressed in very avoidance of sexual situations with her as they develop, and when i really realized i did want them, I just cant seem to get it together mentally enough to make things happen between us. HELP :) I get the sense that i'm pretty good looking but my confidence deserts me when I need it, and i have a lot of anxiety surrounding sex, even with my girlfriend after all this time, and also other situations like the one i'm in now.

Whoa! First thing is, you need to take care of whats going on with you first(depression). If you dont it will arise again no matter who you are dating. Second, shame on you for getting yourself in the relationship with the new girl. Its not fair to her or your girlfriend. First you should be honest with your current girlfriend, tell her about the depressiion and ways you have been feeling, it may change the dynamic of your relationship. If you keep on the track your on, the depression may guilt worse and will be compiled with guilt if you hurt the feeling of the two girls your involved with.