Learn Dutch: De docent had me beter moeten begeleiden, want ik was onervaren. - The instructor should have supervised me better, because I was inexperienced.

This is due to the IPP (Infinitive pro Participio) rule, often called the "two infinitive rule". When a modal verb like moeten helps another verb in a perfect tense (here, begeleiden), Dutch swaps the past participle for an infinitive. So, you get two infinitives at the end (moeten begeleiden) instead of using a past participle like gemoeten.

Does had moeten always mean "should have"? I thought it meant "had to".

When you combine had (or hadden) with moeten and another infinitive, it specifically expresses an unfulfilled past obligation—something that should have happened but didn't. If you just wanted to say the instructor "had to" supervise you (and actually did), you would use the simple past instead: De docent moest me begeleiden.

Why are me and beter placed in the middle, splitting up had and moeten begeleiden?

In a standard Dutch main clause, the conjugated helping verb (had) takes the second position, but all other verbs (moeten begeleiden) are pushed to the very end of the clause. Objects and adverbs like me (me) and beter (better) naturally fit into the "middle field" between them.

I see want means "because". Why didn't it push the verb was to the end of the sentence?