It's such a "DUH" kind of answer, but hear me out. If monotony is the same thing over and over again and again, then maybe don't do the same thing. That's how you have to fight it. Not choosing to do things differently is the same as choosing to stay monotonous. You'll either have to do things differently or just do different things in general.
If it's your comic that you're starting to get tired of thinking about, don't work on it so often! Schedule it out, make yourself work on it 4 days a week maybe. Like I mentioned in a previous topic, working on it so often is only gonna burn you out eventually. On the other hand, you could start a side project as well. It'll have to be more free and easier to work on though, since the romance one you're working on seems take a lot out of you.
As far as friends go, I don't think you should be afraid to tell them that things are getting stale. Let 'em know! They might throw some ideas out there! If you guys do the same things all the time, then do different things. You could also try to find some new friends outside of your usual circle. Get familiar with new people, maybe you'll do new things with them.
For relaxation, you seem to take in a bunch of media. Step outside of your comfort zone! Take a second to watch or listen to different genres! Treat it as exposure and reference! You could also take up different hobbies as well. Learn to play instruments, mess around with voice acting, go hiking, there's a lot you could do!
In essence, if the usual is boring you, do the unusual, I guess!