HIM: Great, on top of a bad week, now I'm a disappointment.
Fights are not meant to be had over text, people! If you are not happy about something, pick up the phone or talk in person. Based on this exchange I'm going to read between the lines and say he blew off plans you two had together. You said you're not happy about it, which is straight-forward enough. He is saying he's been feeling a lot of pressure, maybe at work, and has been stressed/having a rough week. In addition to him feeling under the gun he's bummed he's disappointed you. He basically feels like shit, and this exchange isn't helping. He's into you and does feel bad about letting you down.
Your response: My recommendation is to call him. If you need to cool off first, do it. But better to explain why you're not happy in-depth so he gets what's going on. Also, if you have it in you to forgive, then I'd recommend giving him some reassurance that you have his back. It sounds like things are blowing up for him.
So I don't want to be rude but i would love for you to come straddle and ride my face?
Well at least he isn't intentionally being rude, right? This text comes from a guy you're casually hanging out with because if this was a guy you have been seeing for a while he wouldn't be questioning whether this sort of sext is out of line. He is LITERALLY questioning the statement as he's making it (note the question mark at the end).
More likely the scenario is that he's hitting you up out of the blue. I expect this might even be an online dating message, not a text, and you went out with this guy once, made out after many drinks, and deeply regretted it the next day. This guy doesn't want to date you. Him going down on you is the preamble. He doesn't strike me as the sort of guy who is 100% into giving pleasure. He wants to receive as well.
Your response: You can tell him that's rude. Even a "Don't ever text that again" is an acceptable response. Or maybe you really just want a hook up right now and want to take him up on the offer. In that case you could go with: "Why the question mark?" At least make him be assertive and say what he wants.
Good hearing your voice. I still think about you.
This is from your ex. It must be. Guys you are currently sleeping with do not say this to you. He's saying exactly what he means. You two caught up on Facebook or you ran into him at the gym, and even if you were running errands and paying half-attention to him at the time, he still really appreciated it. He misses you. That doesn't necessarily mean he wants to get back together, but he's also saying that the door is open to that possibility, at least on his end.
Your response: If you like that door being open: "Same." If you want to close that door: "I'm glad we can be friends now."