[HELP] Puppy playing way to aggressively with my other [Smaller] 3-year old dog. Questions

Hey guys,

I'm going to need some help with my new puppy before he gets out of hand!

I got a new puppy (Max, male), who is a rough collie. He's pretty much a dream, at 8 weeks old he has medium energy (like to sleep, or lay most of the day), and he is extremely easy to train also. On the first day I started to teach him Sit, come to me, and look at me. By the second day he was already responding only to my hand movements (commands) about 85-90% of the time.

But there is a MASSIVE problem that started to develop. My girlfriend has a teacup Pomeranian (Pusha), who is 3 years old and is just the SWEETEST thing in the world. We have a running joke saying that the only way she can hurt someone, is if she licks them to death.

The issue is that Max started to play with her, and he keeps biting her, and hurting her. She sequels, cries, and just after a few days she's very scared to be around the puppy. Now I know he's a puppy and he's just playing, but I feel like this is teaching him to become a bully, because he doesn't stop biting her even when she starts to squeal. Also, if this habit sticks with the new pup, than I don't know how we will be able to leave them both at home, without worrying that the puppy will seriously hurt the older dog (Pusha).

Addition info: we invited a friend of ours, who brought her dog. Her dog is about the same size as Pusha, maybe a bit bigger and older. The puppy played with him but did not even try to bite. The pup only bites (play bites) my other dog.

PLEASE advise on what to do, because if I can't solve this problem ASAP, than I'm afraid that Pusha will get injured. She's already starting to get really stressed out and I want for both of my dogs to feel happy and protected at home.

And in-before anyone says that we should take him to puppy play dates, we can't. He doesn't have all of his shots yet, so it's going to be another 3-4 weeks before I can take him to socialize with other puppies. I already looked into all the puppy playtime a around my city, and all of them require your puppy to be fully vaccinated.

No, Stop, Heal and Sit commands.
Past that a solid off command.

Until you have that down redirection and separation.
Doubt it is aggression, more likely natural prey drive, or rough play because the other dog can not do a real correction to teach the pup.

My last mastiff DaVader had this issue at around 10 or 12 weeks because he just did know his size, with a dachshund, he loved the dog, but could not have 40+ pounds of puppy jumping on 12 pounds of small dog.

I would use a baby gate to keep them apart without either of them having to feel excluded. Until the puppy has learned how to respect the smaller dog, and play more gently, I would only allow them to be loose together while there was someone present to act as a referee.

Teach him the "gentle" command let him play and the moment he gets too rough, quietly and calmly intervene and separate him till he’s calmed down. Then when he is more relaxed let them play again, firmly using gentle keep repeating until he associates the word with gentle play.

I also use the word gentle when they start the mouthing stage.

Thank you for all your replies.

I think it's better to be safe than sorry, we will keep them separated when they start to play.

The funny thing that some times, the Pom will actually start the play session (she started doing that yesterday and today), but it still turns into a problem pretty quickly because the puppy can't control himself.