confused and hurt

I am 23 years old my boy friend and I have been dating for over a year now but I've known him for quite sometime now as he was my high shool teacher the thing is that I love him more than I could ever say in a way that at some point I left my previous relationship to be with him. I've always had issues trusting him but was not sure why but now I know . Sometime ago he borrowed my computer as his had a problem and at some point used it to log into facebook and never logged out so when I went in I opened his page and discovered he has up to 6 affairs apart from me. I don't get this . These woman are from other towns yes he leaves sometimes he and I spend almost of the time together when his not working he loves me and we talk a lot about the future and now with all this happening I have no clue what to do because I really love this man. And now my ex he also wants to come back in my life I don't love him like I love this guy but he has a lot to offer financialy and could really help me progress life wise he has several businesses and at this point I'm thinking of going back to him .even this guy I'm dating is always broke which I think he spends his money on girls but its not about money I'll choose him anytime whether broke or not but this issue has made me change my perception about love what should I do really