I’ve never returned or rehomed a fish but it’s an option. I do admire your spirit!!
Just don’t wait until he gets big to move him. Not sure how much experience you have but, while a fish will limit its outer growth to suit the environment, their insides don’t and it can be painful for them.
On the plus side a 55 gallon tank is much easier to maintain!
Not much experience I’ve kept a guppy tank for about 6 months and have had bettas but that’s all. Unfortunately I live in a condo so I can’t get a big tank the max they allow is 20g but I’m moving in July do you think he’ll be ok till then, if not I’ll see if the store will take him back
Gosh he’ll be fine until July. The thing you have to consider I guess is your other stock and if his eventual size will be problematic for them in the long run.
I have no experience with kissing gouramis but have read that their temperaments can be ... bullyish. Even smaller gouramis can present with less than community tank worthy behaviour. Heavy planting with lots of hiding places can help diminish this.
I’d read up on them and decide if he will be a long term fit for you and your other stock. He might also be a peaceful giant (or like 1/6 of my Bolivian rams, a complete dink you have to separate from everyone)
Edited to add: Don’t worry about your experience level! You have a great resource here and everyone started somewhere.
Kissing gourami often do that as a sign of aggression, have you ever seen two fight? It's part of how they get their name because they lip lock and it looks like kissing... very deceiving. And dang you're an awesome person most of these guys don't get anywhere near the right care and you're totally willing to give him the right tank and everything when you can. That's really great! Also, moving tanks is tricky but a lot of people on here have great experience doing so, so they'll be able to help when the time comes. Good luck!