Wellll, I'm not an INFJ, but holy shit do I rebound!! I need the validation of feeling wanted, particularly when I'm at my lowest and going through a breakup. It really helps me heal bc my self-worth takes a huge hit when a relationship ends, and starting a new relationship with someone else can be a huge confidence booster.
I never understood why people are soooo negative about rebound relationships. I mean really, it might last or it might not, but if it's fulfilling a need, why deny yourself? If you're going into it knowing that it's not serious or that it's only going to be short-term, of course be honest with the other party about this. Should also let him know you're going through a breakup--I don't think it's fair not to.
The only concern I ever felt w/r/t rebound relationships is this: it can be hard for the other party to accept you at your strongest when they've only known you at your weakest. There will always be people who don't necessarily want to build you up but want you to remain insecure bc this makes them feel powerful. Ppl can be especially vulnerable to these types when going through a breakup.
Not only that, but ppl are just different when they're at their best than when they're struggling with insecurities. When I'm depressed, for example, I don't even function as the same personality type (I become very introverted, as you know), so if you intend for the "rebound" to last, the other person will have to be able to adapt as you gain your strength back AND will have to accept and encourage you to be strong and happy. If he can't, you have to cut him loose.