Good luck op 
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I'm no expert but I am around teens a lot. I know it's a shock, but don't be too hard on your son. There may have been some coercion going on. (And the fact that the US boy was wearing a hoodie and sunglasses suggests something dodgy to me.) You don't know who was encouraging who and for what purpose.
Anyway, I'm glad you managed to get a hold of the situation and stop communication between them. Obviously, I haven't read the context of the texts, but I would be more alarmed and cross with my DC for not recognising the risks tbh.
Also (as a parent of teens, and someone who volunteers with teens ) there is a lot of "trying on of different personas" at that age, and especially among boys, a lot of bluffing and pretending to be more mature than they actually are.
It's good that your DH is on board and don't be too hard on yourself either. It's the wild west out there in terms of the Internet. It's very hard for parents to keep on top of it all. Now most communication is done via private smart phones, we have very little control over who is influencing our DC. It's bloody scary! It's also a shock when our children turn in to fully raging adolescents with hormones!
In a way, this could end up to be a good thing. Hopefully your DS will come to understand that he put himself in danger and will be more careful in future. And you and your DH will be monitoring things going forward. And you will hopefully be able to keep the lines of communication open between you.
If your son is gay, he may be feeling confused and anxious, and curious, which is what may have led him in to this situation in the first place. It's important he gets his information from the right sources, so please give him the time and space to speak to you. Maybe when the tension over this has died down, invent an errand to collect something, take him on a long drive with a lure of a burger on the way back, then he can talk freely without having to look at you face to face