CSS - Align big Element right of multiple smaller Rows - html

Question

I have a form with multiple inputs.
All of those inputs are Dropdowns, Checkboxes, short Texts, etc. Except one which can be come quite large (textarea). I want all the smaller Inputs on the left side of the Page and the textarea on the right side of the Page.
The Textarea is supposed to have the same height as all the elements on the right side and take roughly half of the Pages width.
My problem is now that I am unable to properly add the Textarea to the right Side. When I use "float:right" then it either has an huge gap between the smaller Elements and itself, or it is small and when I make it bigger then the small Elements become smaller. Or it has the correct size, but then it only has one Element on the left side and every other Element comes after the Textarea has ended.
<form method="post">
<input asp-for="ID" type="hidden" />
<div asp-validation-summary="All" class="text-danger"></div>
<div class="row " >
<div class="form-group col-md-6">
<label asp-for="Title" class="control-label"></label>
<input asp-for="Title" class="form-control" />
<span asp-validation-for="Title" class="text-danger"></span>
</div>
<div class="form-group col-md-5">
<label asp-for="Comment" class="control-label"></label>
<textarea asp-for="Comment" rows="14" class="form-control" oninput='this.style.height = "";this.style.height = this.scrollHeight + 3 + "px"' height:"100vh">
</textarea>
<span asp-validation-for="Comment" class="text-danger"></span>
</div>
</div>
<div class="row">
<div class="form-group col-md-3">
.....
</div>
<div class="form-group col-md-3">
....
</div>
</div>
<div class="row">
#if (Model.Valid is not null)
{
<div class="form-group col-md-3">
....
</div>
}
<div class="form-group col-md-3">
....
</div>
</div>
<div class="row">
......
<hr />
.....
So, all the smaller Elements are inside the "form-group", which are mostly inside "row". And on the right side I now want the Comment TextArea.
I would prefer a plain Bootstrap Solution (especially since everything else is already working in Bootstrap), but I am open to everything.