Dear Carolyn: I am trying to work through the discovery of an extramarital affair on my husband's part a few months ago. We have been married for over a decade, together over 15 years, and have a child together. I discovered his affair while trying to surprise him with a phone upgrade for Christmas, but I was the one who got the surprise … I had the phone when his 18-year-old, college freshman girlfriend texted him. I was completely taken aback and responded that this was his wife, I was here with his teenage daughter, and could she please tell me what was going on?

Long story short, she had no idea I didn't know about her — he told her I was fine with it — OR that he had a child practically her own age. It was, needless to say, a very tense Christmas.

We've spent time in therapy and trying to work through this, but he's taking his first work trip since I discovered this betrayal and I have no idea how to trust him while he's away next week. What can I do?

— Tense

Tense: You cannot trust him.

Because he’s not trustworthy.

At least, his affair proved you can’t trust him, and you haven’t had enough time and experiences since the affair to serve as proof of anything different.

So don’t be afraid, while he’s gone, to live in that well-earned distrust.

I don’t mean you should act on it — that’s awful, attempting to monitor the behavior of a fellow adult. Awful and ineffective. I’m just saying, know you can’t assume the best of him without lying to yourself.

Obviously, just sitting home imagining the worst is miserable. So, do this at the same time, full force: Trust yourself.

Whether he’s home with you or away on work trips, trust that you will be okay.

Whether he uses the trip to cheat again or not, you will be okay.

Whether he’s otherwise faithful to you or not from now on, you will be okay.

Whether you find a way to trust him again or not, you will be okay.

Whether your marriage survives or not, you will be okay.

A 15-plus-year commitment and a child are deep investments you’ve made in him, which I don’t minimize at all. However this turns out, you’re feeling a pain that won’t soon fade.

But you are still you. With him, without him. Your memories are still yours, and the good days of your marriage are still yours to recall fondly. Your daughter is still yours and his, and your job is still to bring the best of yourself to raising her, especially as you guide her through this.

And your future is still yours. Arguably even more so if your marriage ends than if it endures.

Whichever way all of this goes, expect a future different from the one you imagined for yourself — because you’re different now from the person you were before your discovery.

If pain is the only part of this transformation you can really feel right now, that’s normal. But that will also eventually pass, with time, help or both — and when the pain no longer blocks your view, I hope you can start to see new possibilities. A version of you that is wiser, tougher, more empathetic, less tempted by easy assumptions, wider awake: That’s a possible outcome for you, from all of this.

And the decisions this new person makes might ultimately feel better on you than whatever else you were headed to before.

But I’m getting ahead of myself. For now, whenever you feel yourself getting stuck on not trusting your husband, just bring yourself back to this: “I trust myself.” To get through this, to make good decisions, to be a good parent, to be okay.

Hi, Carolyn: My mother-in-law passed away a few months ago. My spouse's 20-something sibling had been living in the family home to take care of Mom. Sibling understandably didn't want to go back to that empty house, so stayed with us.

Sibling is still staying with us now, indefinitely. I really, truly am fine with this situation. Sibling is easy to live with, we have the space and sibling pays for their share of utilities. Spouse and sibling find comfort in each other as they adjust to life without their mom. None of us assumes the arrangement is permanent, but we're all okay with it for now.

Friends and acquaintances ask me in a judge-y tone if sibling is still living with us, and give me advice on how to get rid of unwanted free riders. Some say I'm a saint for putting up with it. Any responses that will stop the judging, or at least get them to stop asking?

— We're All Fine, Really!

We’re All Fine, Really!: What a compassionate problem to have.

For repetitive problems, I recommend repetitive solutions. For this one: “You’re misreading this — I want Sib with us.” Verbatim. Every time.

Good for you.

Write to Carolyn Hax at tellme@washpost.com. Get her column delivered to your inbox each morning at wapo.st/haxpost.