Lifestyle tips

First, to get some context on this ai looked for what else you had posted, and I saw that a year ago your bf had just introduced you to his fetish and you were just getting your mind around it. So I'm glad to see that you are stil together, and that you are ready to tease him!

Ok, so I have more questions than answers for you, for now. There is really two meanings of teasing, one where there is some humiliation involved (and some people like getting that from someone they trust), and the other is more like hints of future pleasures.

For example, let's say his pants are getting tight due to gaining.
-The first type would be to get him to wear those tight pants and take him out to eat a bunch, tell him how it looks like he is going to pop a button, how everyone can see that the piggy is getting too fat for his pants, maybe eventually have him unbutton them and have to walk out that way, showing everyone that he can't even close his pants anymore.
- the second type would be to take him shopping for me pants, and get him to try on not just one size bigger but also two sizes bigger, speculate about how long it will be until he needs that yet larger size, check the slack and talk about how far he a will look once he fills those, and how much you are going to have to get him to eat to get there.

Know which type he wants! Or if in doubt stuck with the second.

And then, just because he wants both of you to gain together doesn't mean that you have to agree. You could decide that you are ok with him gaining but that you don't want to get any bigger. Some of that is just communication and negotiation, but it changes the teasing too. Like if both gaining tease him about needing to reinforce the bed frame soon, if you only want him to gain, tease him about how long it will be before he is heavier than you. (Side note: most people who are into mutual gain have a variety of fat related kinks, so if you don't support all of them that is probably ok so long as you support some of them)