Moving too quick

Basically my ex and I split up last year after a 4 year relationship we have a daughter together were only young I'm 19 she's the same age. Basically we were young I know but after a drunken night we were out she declared her love for me and 6 days later she's going with this other guy then 3 months later they get there own house and my daughter starts calling the new BF dad she still does occasionally but there engaged Aswell since last month and they've gotten tattoos of each other and the date they got together...I'm just curious because I find it very quick as a 21 and 19 year old to have done so much in the space of 1 year like engagement,2 holidays abroad,moving in together and tattoos i just want to know are them relationships normal and do they last because my daughter has really taken to this guy and I know I don't like him because he spends so much more time with her than I do but that's natural for dads to feel that way but he is a good guy to them both I just think there still very young to be making so much commitments I wouldn't like to see everything burnout and then they break up and my daughter has to see the fighting and drama....If anyone can help me even make sense of why people move that quick it would be gratuitously appreciated :)

Hi I'm in the same situation just split with my ex bf of 6 years and we have a almost 10 mnth old son he moved on fast like 3 4 weeks after we broke up he met her on a online dating site desperate I say we have had ex sex whilst he was dating this other girl because he still over me but come last Wednesday we had sex and he then realized he no longer loved me Friday just gone he tells me he doesn't love me anymore and he's in love with his new gf I was so angry and hurt I will be for a very long time because I still have to see him because of our son I'm not coping to well ATM with all of it and he knows and I bet he's happy that I'm struggling with it. I left him because I was depressed in happy wasn't attracted to him anymore then when he found someone new I wanted him back he was going to give me another chance because he was unsure of what he wanted but he changed his mind I was upset and hurt I cheated on him throughout the relationship because he never gave me enough attention I'm not a attention seeker but while he wasn't giving me any other guys were he lied to me at times he'd get home from work and straight on the Xbox wouldn't even help me look after our son at times too but overall I still love him and I would do anything to have him trust me again and have him back with me so we can be a family hey nobody's perfect everyone has there ups and downs right it's hard that I can't avoid him because of our son he turns up to my place covered in blood clots on his neck from his new gf gosh I hate her and deep down I hate him but love him too I'm just really upset and hurt that's all

I was with my ex for two years we have a four year old daughter together we split up over two years ago I know that's a long time, but I still truly love her with all my heart, for the last year I have seen her almost every day she stays at my house for hours spending time with our daughter I was always scared to show her that I still love just in case I ruined things plus I'm quite shy lol I always thought give it more time there's still hope here, well she's met a new man and I don't see her anymore only when she drops my daughter off she hardily speaks to me too, my heart is breaking I'm very depressed its like a break up all over again I love her so much, is there any hope? Is there anything I can do to get her back? Please help!