He would constantly wind me up by laying on my to trap me, tickling me, pulling duvet over my head whilst i struggle and beg him not to. hes always done this stuff and its usually funny. But he just seems to not know what stop means anymore and will carry on whilst I'm visibly frustrated and upset
Sorry, but that's the point OP. You're quite young so haven't had as much time to absorb the experiences of other women yet, so I hope you'll take me seriously when I say this. Abusive men will sometimes tickle, sit on or physically dominate their female partners in order to subtly let them know who's boss. The message they're sending out is 'Look, I'm stronger than you, and I can overpower you and dominate you any time I want......just remember that'. It's a reminder of who's in charge. It could be that he's badly socialised with women or treats you like a sibling, but I would really advise that you take what I've said seriously.
Stop giving him money. Now. He sounds like an alcoholic, maybe a functioning one, and you are funding his habit.
You are of the generation where people talk over and over about mental health, and the result of that is that people, especially women, feel the need to support their partners mental health issues at great cost to their own health & sanity. The issue of women looking after and fawning over their horrible husbands has always been an issue because women have been traditionally encouraged to be nurturing, patient and helpful, but now it's taking on a new form. Do not believe the narrative that you are somehow responsible for him or that you aren't being supportive enough. His mental health issues are his mental health issues, not yours.
Also, you say mental health....are you sure that's not a euphemism for a dominant, immature asshole who's using his girlfriend for alcohol money? I know this isn't the full picture. I know I don't know his good sides, that I haven't seen him smile or how nice he is in other ways to you. I know I don't have the full picture, but I just hope you will absorb this often repeated statement on Mumsnet -
Women should not be rehab centres for badly raised or damaged men
Please, for your sake, stop feeling sorry for him, stop giving him money, and stop infantalising him. He is not your child or patient. It's so sad and pull on one's heartstrings to see someone going downhills, but do not be dragged down with someone who does not take action to help themselves. You are still so young. Please get out now. You will thank yourself so much in a decade's time.