I was with an ENTJ in a long term relationship, that was the most serious one for me so far, we lived together etc.
The start of it was pretty awesome. The best so far. Long term though, I did not find we were on the same wavelength emotionally. That was a major issue for me. Otoh, our way of thinking half matched, half didn't, so that wasn't too bad - it matched or at least was compatible enough when it was about more rational things, e.g. mutual projects or when we did intellectual conversations (those were always awesome!), and not always easily when it was about other things. Not at all matching when it was about things about the relationship itself, which was again a problem for me. I never figured out the solution to that, and I don't actually believe there was one in our case. Now that might just be my brand of realism that you call pessimism, lol.
So don't get me wrong, I don't want to claim that this was type related or to what degree it was type related even, I do know there were other factors playing into this issue. You two seem to be working better based on what you said in the thread. He's making obvious effort to keep communicating, which I think means a lot!, and you said you show how you care about him, etc. Just keep up the attention and the effort at the minimum.
Oh and I did butt heads a lot with the ENTJ too but there were never any hard feelings afterwards. That on its own isn't an issue I would say. But then, neither of us was the grudge holding type and we both could keep arguing in a logical fashion even when angry, which helped.
I dream big and I'm ambitious. He likes the comfortable in life and things I see as rational (Living abroad for a while etc.) is something he says is idealistic. Sometimes when I feel enthusiastic about something, he can completely shoot me down. I've talked to him and he has gotten a lot better, but his pessimism is really shining through. I should mention we have a bit of an age difference. He's in his late 20s.
Dreaming big on its own isn't a problem.
OK the thing is do you feel and show that enthusiasm already before checking out how realistic the thing is? I do shoot down directly or indirectly (by not joining in the enthusiasm) unrealistic ideas very quickly or ideas that could actually be done but a lot needs to be done and it's just not realistic to make the decision to invest that much into that goal. Depending on various factors. This isn't pessimism, this is realism. When I actually committed to something I'm anything but pessimistic.
So for example, living abroad for a while can be possible sure but the devil's in the details.
Overall I would say, you can try and convince him how something would be worth doing but only if it's really something you take seriously yourself, where you know you won't mind the investment and won't stop in the middle of doing it. To convince him, you would need to show him aspects that he didn't think of when evaluating the prospect. It's that weak Ne coupled with lack of experience in the specific area. You can also try to inspire him directly but you will still need to add those aspects to show how it's realistically achievable after all.
Oh and I do not relate to just wanting to live comfortable unless you just mean he's set into some way of living. I don't keep comfort on my mind consciously all day otherwise, I push myself more than that with my goals etc. Now, to change that way of living, there has to be a point, a goal, that then can be integrated into everything else that matters or is already going on for me. Then I'm able to envision this goal and see the concrete steps for it and be committed. Then I can change/upgrade from the current way of living to something else. If this requires moving outside the comfort zone, that's not a problem if there is a point. So for example moving abroad for a while is OK too in this way. But beware, it can take a while to decide on this and getting into it. That on its own shouldn't discourage you.
Adding to this, I do want to say that I absolutely loved it in my relationship with the ENTJ when we had mutual projects with a real goal. So if you can get that going in your relationship, it could be a big boost to it, hopefully.
I don't know how much this helped, if you have specific questions about getting to understand him more deeply, I can answer those but of course it will be applicable only as far as I can relate to your ISTJ.
