Stuck in a sticky situation

Ok so here goes, sorry if it's long winded! I met my partner 10 years ago, I had just split up with my boyfriend and he made me laugh, I wasn't initially attracted to him but I don't always go for looks anyway, he was funny and very confident. I had an 8 year old son at the time and he treated him like his own, we moved in to his house that he inherited of his dad and needed a lot of work doing to it for us to live properly as a family, it was in a bit of a state before I moved in, we remortgaged to enable to fix the house up putting my name on the deeds as I was paying towards the mortgage. He's always been lazy and I was the one doing all the housework etc, even though I was working full time and more hours than him sometimes, this lead to arguments, he was in and out of work, getting the sack due to sick days etc, again leading to more arguments! He eventually settled into another job and things were going ok, I became pregnant which was an accident but I lost it due to ectopic, we were both devastated and this made us think we wanted to have a child so we tried, it took us 3 years but we eventually had our little boy, before we had him our sex life was always amazing, we definitely connected in that sense however since then it has been rubbish! I don't want him to come near me half the time and it's not down to not wanting it but I feel like over the years his ways and lazyness has drained me and I feel like I resent him now! We got engaged when our son was 1, but I think he just did that for formality, he never really mentioned a date kept changing the subject and to be honest I gave up and now don't even know if I want to marry him! I was made redundant after my son was born and ended up going to college to pursue my dream career as a midwife, I am going to university next month to start my course. My partner is very childish sometimes and I chucked him out as he was going out most weekends getting wrecked and ruining days out with our son, I'd had enough, he said he would change and a week later I took him back, while he was gone though I joined a dating app just for a bit of fun and the amount of interest I got was unbelievable, I'm 38 but I don't really look my age, I started chatting to a few different men, some were just after pictures but one in particular just wanted to talk but things lead from there, even after he came back I still chatted to him. My partner was ok for a few weeks but he still doesn't help me around the house and he's slipping back into his old ways which is what always happens with him? I feel like I need to get out but he adores his son and feel devastated that I would be taking him away from the family home, also this house means so much to him I could never take it from him but I need support too with our boys to think about, my eldest who is now 18 adores him and he would be upset If I left, I'm scared I won't be able to cope financially in uni on my own and I can't give it up cause it's took me so long to get into uni to pursue my dream! I can't stop thinking about this person I'm texting and we have spoken on the phone and we connect so much but he's only 25! He thinks I'm amazing and I think he is too! I'm in a mess and don't know what to do? Do I stay in an unhappy relationship to please everyone else? My son is 3 by the way, any advice would be greatly appreciated!