my boyfriend had a girlfriend

right so basically i split up with my boyfriend of 3 years about 2 months ago. i started seeing this guy (he’s 23, i’m 18) i know it’s abit of a bad age gap but i thought oh well he might be more mature but boy was i wrong!!!! after seeing him for a few weeks, went out for a drink together an he met my mates. his ex girlfriend then shown up and started kickin off at me saying he had a girlfriend etc and he was saying no i don’t stop causing shit etc to her so i just ignored her and carried on with my night. we spoke afterwards and after about 3 days i hear nothing off him for a week!!! then his ‘ex girlfriend’ rang me up off his phone kicking off at me saying i was a slag and she was gonna twat me etc and i was like wtf. she then said they’d been together the whole time and we discovered he was with the both of us at the same time!!! he’d come and see me and then stay in hers😂 like what?! who does that😂 i had also slept with him aswell which doesn’t help because other than my ex before him i had never done anything with anyone else and he knew that. she finished him but they’re now back together but he’s trying to be ‘friends’ with me what do i do?! i’ve told him it’s not right because one he treated me like shot and 2 he has a girlfriend but he keeps trying to contact me what do i do?? HELPPPPPP