I know that Le Stag already answered you, but still, here are my two cents about this.
This is a game about hotwifing, even though Laura is technically not MC's wife (not a fan of those acronyms that a lot of people seem to mix up all the time/not understand what they mean here), which means that you've got to have one or several bulls (or an endless parade of one-night stands) for the "wife" to be "hot", or there literally is no game. As you said, Mike is out, and whether you decided to block him or not, Oliver hasn't come back yet, so he might as well be out, too. Which leaves Nathan, who is clearly the "safest" bull you can imagine (he's literally been described as Laura's toy and knows that his place in Laura's and MC's relationship is as a human dildo (Oliver was basically here to make him realize that), and besides, he now has an official girlfriend). The way Nathan has been painted screams "won't ever steal your GF" in basically every scene, so if there ever was a bull who poses zero threat to our relationship with Laura, it's him. He's totally, 100% safe, so I have a hard time imagining why some players would "dislike" him, as you said (Oliver, I can easily understand, but Nathan? Every other bull that Laura is liable to meet will probably be worse than him--see Oliver and Mike).
About Nathan possibly fucking Tara, I haven't played 0.22 yet, but I don't buy it for a second. *My* Tara isn't like that (the one in my game, I mean--I wouldn't know about yours, and I'm sure not planning on stealing her away from you

). She's slowly building a rapport with me-as-MC, and I'm pretty sure I'm the only man she's been opening up to (not like that, you pervs--at least, not yet

). In fact, if she agreed to let the girls convince her to let Nathan take pictures of her, (a) it's probably because she knows he's perfectly safe (see previous paragraph) and won't ever attempt anything with her if she doesn't initiate it--which she won't, not at this stage, and (b) there's a good chance that she's doing it to tease me-as-MC by feeding my kink, all the while learning to be more at ease with her own body and sexuality (Nathan is just her camera, just like he is Laura's human dildo), ie she may be doing it more for MC than for herself, even though she may not realize this at this stage (but hey, as I said, I haven't played 0.22 yet, so I guess I may change my tune next week--I would be *very* surprised, though).