I think if "we" want/expect that women will be financially independent, we can't also expect that the man in a relationship will always be the higher earner/provider and will have to accept that if we want to live "equally" with a partner, sometimes we'll have to contribute to shared trips and other costs, just as men have been expected to forever.
However, this man seems to be taking advantage of that and not fulfilling agreements. I wouldn't have lent the money for the first trip. If he couldn't pay, either we wouldn't have gone or I'd have paid for him because I wanted to go on the trip and the alternative was not to go. However, I would only have done that for a man who's honest about it all. I wouldn't have booked another trip knowing he hadn't yet paid for the previous one.
I think the stag is different, as that was for a fixed occasion, I wouldn't object to him prioritising that over another trip with me. I would very much object to him going while claiming he can't pay what he owes me.
Is he saying he can't afford to pay you back each month, or has he just not paid and you haven't felt able to ask?
Anyway the point I was getting to, is my DP earns less than me. I probably pay more than my share in that I'll buy more rounds in the pub to help him out, I'll drive more often for the longer trips, I dont ask him to contribute when we eat at mine, but he wouldn't want me to "pay" for him and has in fact told me when we need to rein in travelling or nights out, when his budget won't stretch.
My choice ultimately will be whether I want a life that has to be restricted to his budget, whether I want to go and do the more expensive things without him, or to pay for him (or leave a good man in the hope of finding someone with more cash).