But, unless I misremember, not with Andras. Alexia and Rowan have to be on the outs for her to get with him, right? I might very well be wrong about this; I don't actually play the game anymore.
What you are describing is entering Andras' NTR path. When she is on his NTR path then yes he is training her to just be a slut for him. But there are many encounter with him that are not part of the NTR path as well.
There are 3 requirements to start the NTR path.
1. A low relationship between Alexia and Rowan
2. Alexia having at least medium corruption
3. Andras having more influence on Alexia than Jezera, and not already being on Jezera's NTR path.
If you don't meet
all those criteria then you wont start the Andras NTR path.
In the event you do trigger his NTR path you have several opportunities to derail it in the first scene. When Rowan asks Alexia to deliver some orders to the orcs, don't insult the orc back, if you do insult the orc then don't turn to Andras for help after the orc almost rapes her, if you do turn to Andras for help then don't meet with him afterwards. If you avoid doing any of those actions you will derail Andras' NTR path and you don't have to worry about Alexia turning in to his personal cumslut by sleeping with Andras anymore.
That said having sex with a demon always raises corruption. It doesn't matter which demon it is. And Andras also has a number of scenes where he is actively trying to drive a wedge between Alexia and Rowan, and if Alexia goes along in those cases it will reduce her relationship with Rowan. But there are also a few opportunities to increase their relationship stat that can be used to boost it back up.
For example, if Andras tells Alexia to suck his dick because he is horny and she agrees, she gains corruption for sucking off a demon. If Andras tells her she should fuck him because her husband is a wimp, and she responds that he's right her husband is a wimp and proceeds to fuck him, she gains corruption for fucking a demon and then she also loses relationship because she is thinking less of Rowan.