A little advice for a 50+ relationship???

I'm in my mid 50's and my Girlfriend is in her late 40's. We've had a rocky relationship, mainly because I've been a little selfish, but I've been seeing a therapist for that. I've recently found out that she's been going to an older man's (mid 80's) home on the weekends. After originally telling me she had been working during this time, I found out where she was going and she came clean. I also found out the gentleman is the financier (bank) for her recently purchased car. She tells me she's going there to help him with his medications and living issues, (laundry and such), and in doing this is paying payments on her car, ($100 per day for helping him). The man has had prostate surgery, and is beyond having sex, so I know that's not going on, (but there are a lot of things an older guy would like to see, it's all in the mind), but it doesn't explain why she didn't tell me the truth to begin with, and why she clearly has a hard time texting or talking to me while she's there. After about 9pm, she will not answer a call or a text while there. What should I do? Do I trust her explaination, or do I believe she's hiding something that's going on??? Please help!

Regardless if you're selfish or not, your GF owes it to your relationship together to be upfront with you with everything she does just as you do. If there's nothing going on between her and the other guy, then it should have not been an effort for her to tell you the circumstances at the beginning. She hid it from you and she lied to you and it's up to you to determine why she did this. If you've had a rocky relationship, then you also need to determine whether it's worth the while and why you need to be with someone who doesn't understand the importance of trust or if their actions are the cumulative result of your rocky relationship.