hey there
im new here also and come asking for help on a similar case, a depressed ex gf :3

she did almost the same with you except with no contact mode out of no where, and then I guess she was with new guy for few months, and she tend to do that I guess before she realize that she cant go on with this deeper, so whe push them away as the same way she pushed me, but I guess in your case I agree with Skeezyks about this part :

they may be just coming together based on their mutual unhappiness, or as a depressed person let alone Weed addict its surely not a good perioed after the person dump someone he loved because he is **** in his opinion and cant do anything, therefore they seek another attention right away, to ease the hole and gap you left, and I see that there seems to be no sexual relation between them, that's why I tend to think its not a sex drive move here, its more of a she seems like a potential target to help.

any way as they said its better off to you with this guy, there's so much for it in him, I don't think its worth to wait and hold for him like im doing since 3 years now for my ex girlfriend right now.

wish you all the best, don't try to compare and say that he dumped me for her, there's no logic in here I guess.