I guess I need to clarify things a little bit more. I did talk to TM about the entire situation about a month or 2 ago. I told him I liked DM, clarifying after that letting him know that I hold a loyalty to his family as a whole over any desire I might have for DM in any way past friends. His reply was "It's all cool man." and "If I got mad about every guy that liked DM, I wouldn't keep any friends at all. It's fine."
I know better than to be flirty or anything else with someone if their partner has no knowledge whatsoever. I also have to add that the basic knowledge of the particular desires is out there to all 4 people involved. Both TM and DM know about HT liking TM and about me liking DM. I made it abundantly clear that HT and I hold a deep respect for their relationship because we value their friendship and AM's well being above all else. While TM doesn't talk about feelings or anything like that, in the very least he knows that without his express blessing in the matter that there will be nothing else that happens along the lines of dating or farther.
Thank you for making me realize that there were things that I had forgotten to put into this to bring a better understanding to anyone looking at it from the outside.