You can't fix a black heart, unless you go back to savefile where Gunnar didn't had a black heart...
On normal Logan route you are able to watch getting Ste naked when you help him at the farm I guess.. Also there is a random chance you can suck a huge thick dick at the gloryhole that could have been Ste's (but we're not sure about that I think).
Also he visits you at home randomly, eating lunch together, it can end up with some cuddles, and kissing if adding aphrodisiac, you can also invite Korg and have some sort of a trio.
Don't think you can change font size..? I play on PC so I don't know for sure..