Staying at my boyfriend's parents house

Ok I need to explain this as I've been thinking about it more recently and feel I need advice on it.

I'm 19 and been with my boyfriend (who's also 19) for 6 months and for after about 2 months we started staying over each other's houses every night. Probably mine about 3 times a week and his 4 times a week.

After about a month it just ended up being me staying at his every night as I think he preferred it and it was easier. So the whole time I've felt bad as I've been worrying how his parents feel about it. I always say to him how bad I feel and if they're ok with it and he says they're fine with it and I don't affect them in any way and don't get in the way.

I only have dinner there once a week or sometimes not at all and I literally have a shower at mine as often as possible so I don't use their water.

They seem fine with me and I'm always very respectful of them, however I really don't want to take the piss as I'm not like that at all.

I'd really appreciate any advice or if you've been in the same situation to let me know. Thank you!